Application of a necking criterion to PET fibers in tension

A criterion to predict instability in rate-dependent materials is developed . It is implemented for PET fibers in tension at three temperatures: 60, 75 , and 80 degrees C. At 60 degrees C, necking is always observed, whereas at 80 degrees C, the deformation is uniform, and 75 degrees C marks a transit ion region, where necking is observed only at higher speeds and the deforma tion is otherwise uniform. As a necessary tool in the implementation of thi s criterion, the stress-strain behavior of PET is modeled using a combinati on of an Eyring process, a Gaussian network, and a linear elastic element. The resulting instability model gives predictions that are generally consis tent with the experimental observations at all temperatures. (C) 1999 John Wiley & Sons, Inc.